Various techniques currently exist for recovery of viscous oil from underground deposits, including recovery of oil from within oil sand and oil carbonate formations which may have a “pay” zone in the range of between 15 m to 200 m thickness, typically commencing 20-500 m beneath the surface.
One such recovery technique is the so-called SAGD technique (“Steam Assisted Gravity Drainage”), such as disclosed in U.S. Pat. No. 5,273,111 to Brannan et al, 1993), which uses an upper and lower pair of vertically-aligned horizontal wells drilled into a “pay” zone. Heated steam is injected into the upper well of such pair of horizontal wells, and thereby into the formation, heating oil within the formation and thereby reducing its viscosity, which heated oil then drains downwardly in the formation and is drawn into and recovered to surface via the lower well of the well pair.
Other recovery techniques utilize in situ combustion of a portion of oil within the formation, wherein an advancing combustion front fuelled by a portion of the oil in the formation heats remaining oil thereby reducing its viscosity, which heated oil is then collected via a horizontal collector well placed low in the formation. An air injector well is used to inject air into the formation and supply air to the combustion front. Two such in situ combustion recovery methods can be found respectively in U.S. Pat. No. 5,626,191 and U.S. Pat. No. 7,841,404. Many other combinations and techniques have been used in the prior art for recovery of oil from oil formations.
Commerically-available computer modelling programs exist for experimentally modelling and predicting the cumulative oil recovery over time from an oil reservoir using a particular oil recovery method, as a means of studying and attempting to determine the most effective method for recovery of oil from a formation.
For example, a number of such computer simulation reservoir modelling software programs which presently exist are as follows:
(i) STARS1 (Steam, Thermal, and Advanced Processes Reservoir Simulator) reservoir modelling software, available from Computer Modeling Group, Ltd., Calgary, Alberta, Canada, 1 Trademark of Computer Modeling Group, Ltd., Calgary, Alberta, for reservoir modelling software
(ii) VIP2 reservoir modelling software, available from Landmark Graphics Corporation, 2 Trademark of Landmark Graphics Corporation for reservoir modelling software
(iii) ECLIPSE3 reservoir modelling software, available from Schlumberger Corp. 3 Trademark of Schlumberger Corp. for reservoir modelling software
In utilizing such reservoir modelling software, the reservoir properties (which may be obtained from core samples or vertical well logs from wells drilled at various locations in the formation, and which can include geologic data, spectral density log (SDL) data, as well as seismic data, may be input into some of such computer modelling software
For example, such reservoir properties, may be, for one computer model of a hydrocarbon formation, as follows:
IllustrativeParameterUnitsValueReservoir PropertiesPay thicknessm30Porosity%30Oil saturation%75Water saturation%20Gas saturationfraction5Horizontal. Permeability ofmD5000formationVertical Permeability ofmD3400formationReservoir pressurekPa3000Rock compressibility/kPa  5 × 106ConductivityJ/m K3.2 × 105Rock Heat capacityJ/m3 K2.5 × 106Oil PropertiesDensitykg/m31009Viscosity, dead oil @ 20 C.cP500,000Average molecular weight oilAMU598Compressibility/kPa1.06E+3
The geological properties are typically entered into geological modelling software such as Petrel™, available from Schlumberger Corp., or Earthmodel™ available from Forgo-Jason. These geological models are typically “upscaled” by combining grid blocks for use in the computer simulation reservoir modelling software.
Seismic data may also be collected by placing an array of hydrophones and geophones at selected locations on the surface of the reservoir, or seismic may be collected on a real-time basis using geophones placed in wells, and are collected over time (known in the industry as 4D seismic). The obtained seismic data may be processed using software programs such as Seisworks and Earthcube available from Landmark Graphics Corp., to obtain hydrocarbon indicators, stratigraphy, and structure useful for computer modelling of hydrocarbon formations undergoing exploitation using one of the several recovery methods including SAGD or in situ combustion.
As noted, for example in US Pub. 20070168170, the log data, core data, and SDL data can be pre-processed using computer programs such as Petroworks4 available from Landmark Graphics Corporation, Prizm5 available from Geographix Inc. (now LMKR Canada Inc.), or DPP6 available from Halliburton, to obtain water and oil saturations, porosity, and clay content of a particular formation. 4 Trademark of Landmark Graphics Corp. for well data pre-processing computer software5 Trademark of LMKR Canada Inc. for well data pre-processing computer software6 Trademark of Halliburton Energy Services Inc. for well data pre-processing computer software
Disadvantageously, however, computer reservoir modelling software (depending on its sophistication and the amount of formation data which may be input) nonetheless cannot entirely predict reservoir performance using various different recovery techniques. Particularly in the case of carbonate reservoirs, such reservoirs are often difficult to model via computer software models. Specifically, carbonate reservoirs have complex and heterogeneous geological and petrophysical characteristics. They are often naturally fractured, and exhibit complex porosity systems and wetability characteristics, which influence drastically their multi-phase flow properties.
Accordingly, there is always some level of disparity of the computer simulated model, as compared to actual results which are ultimately attained in the real-life performance of a physical reservoir. The level of disparity can sometimes be significant, particularly in the case of carbonate reservoirs.
Moreover, real-life reservoirs are each unique in regard to various physical parameters thereof. Due to the permanent change invoked on a real-life reservoir once a single oil recovery method is tested thereon, it is impossible to thereafter conduct a further test on such identical formation, using a different method, to determine which method is better. Such uniqueness and irrevocable changes inflicted on a reservoir when using a particular recovery technique to date has prevented effective comparison of different oil recovery techniques on an individual reservoir on an “apples to apples” basis.
Thus a real need exists in the industry for more accurate and reliable reservoir performance prediction means which better allows for comparison of and optimization of oil recovery techniques from a hydrocarbon reservoir/formation, without having to incur the time and significant expense in physically testing recovery techniques on a real-life reservoirs, and being able to compare recovery techniques on an “apples to apples” basis with regard to the same reservoir.